This invention relates to operation control methods for nuclear reactors, and more particularly it is concerned with an operation control method for a nuclear reactor that can have application in a nuclear reactor performing a daily load follow-up operation in which power control is effected by using control rods and liquid poisons.
A pressure tube type nuclear reactor comprises a multiplicity of pressure tubes having fuel assemblies therein which are mounted in a calandria tank to extend through a moderator contained therein. A coolant flows through the pressure tubes. Power control of this type pressure tube type nuclear reactor is effected by inserting and withdrawing control rods in the moderator between the pressure tubes in the calandria tank, and adjusting the concentration of a liquid poison incorporated in the moderator in the calandria tank.
In recent years, there has been a tendency to adopt a method of operation of a nuclear reactor which aims not only at producing a fixed reactor power for a base load but also at developing a reactor power which may vary depending on a fluctuation in load, by performing a load follow-up operation. The pressure tube type nuclear reactor of the type described hereinabove is not an exception, and research has been conducted into the possibilities of incorporating the load follow-up operation in this type of nuclear reactor. For example, a proposal has been made in Japanese Patent Laid-Open No. 141594/82 to incorporate the load follow-up operation in a pressure tube type nuclear reactor.
The document referred to hereinabove shows in FIG. 5 thereof a load follow-up operation control system for a pressure tube type nuclear reactor which is designed to effect control of operation of a nuclear reactor in a manner to cope with demands for electrical power which vary from daytime to nighttime during a day by increasing power in the daytime and reducing it in the nighttime everyday. In a nuclear reactor using control rods and liquid poison concentration adjustments as control means, such as a pressure tube type nuclear reactor and pressurised-water reactor, control is effected to keep the reactor power in the range of allowable powers between an upper limit line and a lower limit line set above and below, respectively, a power fall line or a predetermined power fall rate (or a power rise line or a predetermined power rise rate) in accordance with a fall (or a rise) of the reactor power.
Load follow-up operation control of a pressure tube type nuclear reactor will be described. In this control process, a high reactor power achieved in the daytime is reduced to a low power level in the nighttime by increasing the concentration of a liquid poison in the calandria tank. Insertion and withdrawal of the control rod are performed only when the reactor power tends to exceed the upper limit line or lower limit line of the range of allowable powers because they cause great damage to the fuel assemblies by bringing about sudden changes in reactor power. Operation of the control rods has a much higher rate of change in reactor power than adjustments of the concentration of the liquid poison, and has the risk of damaging the fuel assemblies in a high nuclear power range. Thus, one should refrain from operating the control rods as much as possible in the high power range.
The load follow-up operation control of the pressure tube type nuclear reactor shown in FIG. 5 of the document referred to hereinabove aims at the reduction of the number of times of operation of the control rods during a load follow-up operation of the reactor. The control is effected by obtaining predicted values of changes with time of the reactivity from changes in the reactor power by using values of the reactor power set beforehand and data for analyzing the dynamic characteristics of the nuclear reactor, splitting the time for effecting power control into time units in accordance with the changing rate of reactivity obtained from the predicted values, and determining optimum values of the quantity of liquid poison to be injected or removed for each time unit, to thereby control the concentration of the liquid poison in the calandria tank to an optimum level at all times. Although this control process has achieved a success in reducing the number of times of operation of the control rods, the control rods are still operated for about 300 times to keep the reactor power to the vicinity of 50% when a load follow-up operation of the reactor is performed while maintaining the reactor power at a 50% level.